1. Field of the Invention
The invention relates to a waste gate actuator for an exhaust gas turbocharger, comprising an actuator housing and an actuator cover, wherein an element for actuating the waste gate valve and electronic components for controlling the element for actuating the waste gate valve are arranged in the waste gate actuator.
2. Description of the Prior Art
The power generated by an internal combustion engine depends on the air mass and the quantity of fuel which can be fed to the internal combustion engine. If it is desired to increase the power of the internal combustion engine, it is necessary to feed in more combustion air and fuel. This increase in power is brought about in an induction engine by increasing the cubic capacity or by raising the rotational speed. However, increasing the cubic capacity basically produces internal combustion engines which are relatively heavy and have relatively large dimensions and are therefore expensive. Raising the rotational speed entails considerable problems and disadvantages, particularly in relatively large internal combustion engines.
A technical solution which is often adopted in order to increase the power of an internal combustion engine is supercharging. This refers to the precompression of the combustion air by an exhaust gas turbocharger or by a compressor which is driven mechanically by the engine. An exhaust gas turbocharger is essentially composed of a compressor and a turbine, which are connected to a common shaft and rotate at the same rotational speed. The turbine converts the energy which is normally output uselessly through the exhaust gas into a rotational energy, and said turbine drives the compressor. The compressor sucks in fresh air and feeds the pre-compressed air to the individual cylinders of the engine. An increased quantity of fuel can be fed to the relatively large quantity of air in the cylinders, as a result of which the internal combustion engine outputs more power. The combustion process is additionally favorably influenced, with the effect that the internal combustion engine has a higher overall efficiency level. Furthermore, the torque profile of an internal combustion engine, which is supercharged with a turbocharger can be made extremely favorable.
Series induction motors from vehicle manufacturers can be significantly optimized by using an exhaust gas turbocharger without intervening structurally to a large extent in the internal combustion engine. Supercharged internal combustion engines generally have a relatively low specific fuel consumption and have lower emissions of pollutants. Furthermore, turbo engines are generally quieter than induction engines with the same power level since the exhaust gas turbocharger itself acts as an additional silencer.
In internal combustion engines with a large operating rotational speed range, for example in internal combustion engines for passenger cars, a high charging pressure is already required at low rotational speeds of the engine. For this purpose, a charging pressure control valve, referred to as a waste gate valve, is introduced into these turbochargers. By selecting a corresponding turbine casing, a high charging pressure is built up even at low rotational speeds of the engine. The waste gate valve then limits the charging pressure to a constant value as the rotational speed of the engine increases.
As the quantity of exhaust gas increases, the maximum permissible rotational speed of the combination of the turbine wheel, the compressor wheel and the turboshaft, which is also referred to as the rotating parts of the exhaust gas turbocharger, is exceeded. If the rotational speed of the rotating parts were to be unacceptably exceeded, the rotating parts would be destroyed, which would amount to the turbocharger being totally written off. Particularly modern and small turbochargers with significantly smaller turbine wheel diameters and compressor wheel diameters, which have an improved rotational acceleration behavior due to a considerably smaller moment of mass inertia, are affected by the problem of the maximum rotational speed being exceeded. Depending on the configuration of the turbocharger, complete destruction of the turbocharger occurs even if the rotational speed limit is exceeded by only approximately 5%.
Waste gate valves which, according to the prior art are controlled by a signal resulting from the generated charging pressure, have proven useful for limiting the rotational speed. If the charging pressure exceeds a predefined threshold value, the waste gate valve opens and conducts part of the mass flow of exhaust gas past the turbine. Because of the reduced mass flow, said turbine takes up less power and the compressor power is reduced to the same degree. The charging pressure and the rotational speed of the turbine wheel and of the compressor wheel are reduced. However, this control is relatively slow acting since the build-up in pressure, when the rotational speed of the rotating parts is exceeded, occurs with a time delay. For this reason, the control of the rotational speed of the turbocharger with monitoring of the charging pressure must occur in the highly dynamic range (load change) by correspondingly reducing the charging pressure at an early point, which leads to a loss of efficiency.